Saw this post and had to reply.
First of all, if you're not getting a full cat back Apexi A1, there's no reason to get it at all. The only thing that the muffler (alone) will do is make you car louder. With the wider piping you will increase your air flow giving your car that sexy sound and the horse power that you want and/or need.
Dual Apexi vs. single doesn't have that much difference in horse power. You're already getting the air flow that you need from the single cat back exhaust, so if you get the dual, the only difference you will see is in your wallet. Hope I didn't reply after you got your exhaust and that I may have been of some service.
